Abstract:

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The gelation process is of importance for the structure and texture of the silica particle
and further functionalization in the area of biomedical application. In a base-catalysis process the
sodium phosphate or plus calcium nitrate salts could be added to induce the gelling velocity and
particle size distribution. Multivalent anions (phosphate ions) or dication (calcium ions) induce the
microscopic phase separation and accelerate gelation of silica sol. Furthermore, the composite silica
nanospheres show excellent monodispersibility as well as pH-stability in the simulated body fluids
or Tris-HCl buffer solution, which will help to surface modification and functionalization in the
biomolecule-existing environments.

Abstract: The feasibility of bubble templating method to prepare hollow particles was tested in this
paper by passing a bubble into a silica sol. The silica sol was prepared by mixing TEOS, water,
alcohol and hydrochloric acid. To control the gel point, the reactants and their concentrations were
varied in each experiment. After the sol was prepared, an ammonia bubble was introduced into the
prepared sol through a capillary tube. With the catalysis of ammonia, the silica sol gelled on the
surface of bubble and formed a hollow gel particle. The nucleation of silica gel on the surface of
bubble was discussed in this paper.

Abstract: Silica aerogels were synthesized from hybrid silicon sources of TEOS and acid silica sol by
two-step sol-gel method and supercritical drying. Different chemical compositions of the starting solution
were altered in order to make an insight into the relationship between process parameters and the
microstructural characteristics of resulting silica aerogels. The results indicate that a certain amount of
acid silica sol may promote the gelation process while excessive nano-scaled silica particles easily result
in dense structure and low specific surface area. The gelation time increases with the increasing water
amount. Excessive water will lead to weak network structure of silica gels and thus larger shrinkage and
lower porosity of the resulting silica aerogels.

Abstract: Consolidation of cements and geopolymers can be explained by the formation of alkali
silicate or alumino-silicate gels formed in situ during materials setting. To control such a system, a
study concerning the use of sodium silicate gel as binder was initiated to manufacture consolidated
materials with different size distribution of silica. The gels used as precursor of binder were
synthesised by acidifying with hydrochloric acid, a concentrated sodium silicate. Consolidated
materials were obtained by mixing the previous solution before gelation with granular materials
(fine silica powder and sands).
The existence domain of consolidated materials depends on the size distribution of sand.
Consolidation of material is strong when the amount of silica is high. This result suggests a
dissolution / precipitation reaction between gel and silica. Therefore, consolidation could be
explained by the dissolution of small particles of silica and their precipitation into the grain
boundary of sand. Mechanical properties are closed to those of cement materials.

Abstract: Silk hydrogels have mechanical properties and structural features that are similar to load-bearing soft tissues, and can be implanted for tissue restoration. In the present study, we investigate silk fibroin sol-gel transition processes in detail. The effect of different surfactants and high temperature pretreatment were studied detailedly. Based on the study, a mechanism was summarized. The result showed that the surfactant accelerated sol-gel transitions while heat pretreatment decelerated sol-gel transitions. Gelation time was decreased to several hours when added surfactant with negative charge. On the contrary, gelation time was increased to dozens of days when extended the time of high-temperature processing. Upon gelation, a random coil structure of the silk fibroin was transformed into a β-sheet structure.

Abstract: The effects of gellan gum and calcium ions concentration on gelation characteristics and rheological behavior were investigated using TA(texture analysis)and mechanical rheometer which monitored respectively press strength and the evolution of G′. At a premium gellan gum content of 0.02g in 100ml buffer solution, increasing calcium ions concentration led to an increase in the gelation strength, but when calcium ions content reached a critical concentration values range from 0.015% to 0.02%, gelation strength begin to decrease. While in the same content of calcium ions, calcium lactate exhibits grater effects on gelation strength than calcium chloride. The temperature at the onset of gelation and the gelation rates showed an increase with the increasing of gellen and calcium ions content. At the same calcium ions concentration, the evolution of modulus storage (G′), gel temperature and rate are higher with the addition of calcium lactate than using calcium chloride. Our study indicated exponential relationship between gelling temperature (gelling rate) and calcium concentration.